Chlorofluorocarbons (hereinafter, CFCs) have been widely used as blowing agents for producing polymeric foams. However, in recent years, CFCs have been shown to contribute to depletion of the earth's ozone layer (due to their chlorine content), as well as to global warming (due to their long atmospheric lifetimes). Thus, there has been general agreement that replacements are needed. (See "Montreal Protocol on Substances That Deplete the Ozone Layer," Copenhagen Amendments, United Nations Environment Program, 1992.)
One approach to developing CFC replacements has been to substitute hydrogen atoms for chlorine atoms so as to provide hydrochlorofluorocarbons (hereinafter, HCFCs) or hydrofluorocarbons (hereinafter, HFCs). HCFCs and HFCs have lower ozone depletion potentials (that of HFCs being zero) and shorter atmospheric lifetimes than CFCs, but their performance as blowing agents is inferior to that of CFCs. (See, e.g., the discussion by D. Rosbotham et al. in "HFC-134a--A Zero O.D.P. Option for Rigid Polyurethane Foam," Proceedings of the SPI 34th Annual Polyurethane Technical/Marketing Conference, New Orleans, Louisiana, Oct. 21-24, 1992. ) Consequently, the search for true replacements has continued.
Perfluorochemicals, as well as various partially-fluorinated materials, have recently been suggested for use in foam blowing. For example, U.S. Pat. Nos. 5,210,106 and 5,211,873 (Dams et al.) disclose blowing agent emulsions comprising one or more low boiling, chlorine-free, perfluorinated compounds.
U.S. Pat. No. 5,162,384 (Owens et al.) describes a blowing agent emulsion comprising at least one low boiling, perfluorinated, N-aliphatic, cyclic 1,3- or 1,4-aminoether.
EP 439,283 (BP Chemicals Limited) discloses blowing agents comprising perfluoro- or partially fluorinated-(cyclo)alkanes.
EP 416,777 (Imperial Chemical Industries) describes a method for the preparation of a polymeric foam which comprises vaporising a fluorine-containing ether in the presence of a foamable polymer or the precursors of a foamable polymer.
U.S. Pat. Nos. 4,972,002 and 5,187,206 (Volkert) disclose blowing agents comprising low-boiling, fluorinated or perfluorinated hydrocarbons and tertiary alkylamines.
U.S. Pat. No. 4,981,879 (Snider) describes the use of perfluorinated hydrocarbons in foam preparation to enhance the thermal insulating properties of the resulting foams.
U.S. Pat. No. 4,997,706 (Smits et al.) discloses the use of a C.sub.2-6 polyfluorocarbon compound containing no chlorine or bromine atoms as a physical blowing agent in the preparation of rigid, closed-cell, polymer foams.
CA 2,037, 587 (Hoechst Aktiengesellschaft) describes a process for the manufacture of foams with the aid of blowing agents containing fluoroalkanes and fluorinated ethers.
U.S. Pat. No. 4,972,003 (Grunbauer et al.) discloses a blowing agent composition comprising one or more organic compounds, particularly halocarbons, having a boiling point of less than or equal to 272K at atmospheric pressure, which composition is substantially free of organic compounds having a boiling point of 273K or greater.
U.S. Pat. No. 5,205,956 (Volkert et al.) discloses a process for the production of plastic foams, in which the blowing agent used is at least one vinylfluoroalkane.
Japanese Patent Publication Nos. 51-79042, 51-79043, and 51-79045 (Daikin Kogyo KK.) disclose the use of 2-trifluoromethyl-3,3,3-trifluoro-1-propene, cis-1,1,1,4,4,4-hexafluoro-2- butene, and 4-hydro-heptafluoro-1-butene, respectively, as foaming agents.